Electricity production by means of wind energy is among renewable energy sources that had the most development in recent years. This growth is due to this source's attractive characteristics, mainly when the ecological benefits are considered, such as the low environmental impact, non-emission of gases, radioactive particles or residues. Furthermore, arrangements adopted in wind energy plants allow rapid addition of extra modules in cases of increase in energy demand. In addition, since the base of the support structures for the wind turbines occupies reduced area, the adjacent areas can be used for other purposes, like agriculture.
Said wind turbines are basically made up of a support structure, such as a tower; the rotor, usually made up of three blades connected to a central disk; besides the power generator itself, which stays inside a capsule called nacelle, and transmission and control mechanisms.
As a result of said increase in the demand for a clean, safe and renewable electric power source, there is a strong need to optimize all constructive aspects of wind turbines, so as to provide a greater electric power generating capacity. Therefore, there is a tendency for economically feasible solutions to end up resulting in rotors with increasingly greater dimensions. These improvements, however, cause several difficulties in the logistic processes, among which are particularly highlighted the handling, storage and transportation of the structures, by land, sea or air.
More specifically, one of the reasons for increase in rotor dimensions is to increase efficiency of wind generators, in addition to increase in the longitudinal dimension, the blades of the wind turbine rotors are preferably designed with a chord (i.e. width of the blade profile) in the blade root (i.e. region near the rotor center) with high dimension. This way, these blades have high cost of transport due to the singular geometry, with great longitudinal and transversal dimensions, requiring special cares to prevent damages during the logistic procedures. For land transport, for example, blades with transversal dimensions greater than three (3) meters can no longer transit freely in the road systems of several countries. Today, blades with greater dimensions already exceed this limit and suffer many restrictions to reach the installation site of the wind turbine. Furthermore, the larger the blades the greater the problems to use standard handling equipment such as hoists; as well as standard storage and transport packages. On the other hand, when changes are made in the blades only in function of problems in the logistic procedures, without concern with issues of performance and aerodynamic control, there is a great loss in the capacity and versatility of the power generation of wind turbines. There are therefore, in the prior art, several constructive arrangements that aim at obtaining a blade of easy transport, storage and handling; while other arrangements aim at obtaining only improvements in performance and aerodynamic control. Few solutions, however, are concerned with both factors at the same time.
For example, the patent application published under No. US2004/0105752 describes a rotor blade for wind turbine with an acting surface of the wind with a variable area Said surface is obtained by means of a blade made up of a deformable or movable part with, consequently, less load for installation and greater ease of transport. In a better mode of execution described in this application, a part of the surface can be made of a deformable material forming a closed recipient. In this case, the recipient can be filled by a gaseous medium with a predetermined pressure. This way, this inflatable surface can be emptied during transport or in situations of extreme winds, reducing the area of the wind's operation. As a result, the load on the other components can be reduced, including on the tower. A similar solution is adopted in the patent application published under No. DE10233102A1.
Other types of arrangements found in the prior art, however, more specifically directed toward problems of performance and aerodynamic control, consider the use of high-lift devices, such as flaps, both in fixed or rotary airplane wings and in wind turbines, such as in the patent application published under No. EP152443 μl, which has other similarities with the solutions, adopted in U.S. Pat. Nos. 5,527,151 and 5,570,859 and in the patent application published under No. ES2035118T. U.S. Pat. No. 5,527,151 describes an aileron embodiment for wind turbine rotors, said aileron having a bottom surface such that it does not protrude in the airflow. The movement is executed around the center of rotation located within the envelope of the aileron, so as to allow positive control of the rotation. This movement of the aileron allows positioning it such that it creates enough drag to stop rotation of the rotor. U.S. Pat. No. 5,570,859 describes a blade spoiler for wind turbines or wings that controls or influences the airflow over the blade or wing surface. The spoiler can turn around in a way that its projects the anterior end over the low-pressure region at the same time that the posterior end is projected over the high-pressure region. When the spoiler is fully pivoted (orthogonal to the blade or wing longitudinal plane), it works as a brake, while when it is partially pivoted, it works as a power modulator. Meanwhile, patent No. ES2035118T describes a streamlined body with variable profile, having a stretched membrane over the surface so as to allow an inflated or water-filled configuration to vary the profile. Said streamlined body has a shape similar to that of an airplane wing, comprising an aileron and a small plate. This way, the body allows greater curvature of the profile, enabling increase of lift. Additional variations of high-lift device arrangements in blades are also foreseen in the U.S. Pat. No. 4,423,333, in the patent application published under No. US2003/0091436A1 and in the international pub-lications under No. WO2004/099608A1, WO03/076802A1 and WO2005/040559A1.
The patent application published under No. CA2425447A1 describes a blade for applications such as in wind turbines, made up of a main airfoil and a smaller secondary airfoil, preferably in the canard configuration. The airfoils are joined by means of at least two structural elements, resistant to vibrations and with aerodynamic profile perpendicular to the longitudinal axis of the airfoils, distributed along the secondary airfoil. In order to guarantee aerodynamic stability, the blade is balanced by means of rotation in relation to the longitudinal axis.
Other devices that adopt elements adjacent to the blades are found in patents No. LV12775(W002053908A1); LV12972and LV13091, in which the use of blades with cascaded profiles is proposed, in order to increase energy use with reduction of the starting wind. While in documents No. LV12775and LV 12972, the arrangement is appropriate for vertical axis wind turbines, in document No. LV 13091the use of a configuration similar to that of document No. LV12972is proposed, but with a horizontal axis of rotations. However, although the axis of rotation proposed is horizontal, the solution adopted has the rotation of cascaded profiles parallel to the axis of rotation. A similar solution is adopted in the patent application published under No. JP2005-90332
Finally, another configuration is foreseen in the patent application published under No. DE4428731, which describes a blade with variable length, obtained by means of an external blade with hollow profile, inside which there is a section of telescopic blade over at least part of the extension, which can move over a fixed rail outwards of the external blade. Therefore, by modifying its length, it is possible to meet different transport conditions, as well as varied wind conditions. A similar result is obtained in the international publication under No. WO20061008327A1 and in the patent application published under No. EP1375911A1.